Smart client assembly wont download to client until all opened explores closed.

We found out (using gacutil /ldl) that new versions of smart client assembly aren't being download to the client although we place in the server assembly with newer time stamp. After long research we found out that if one of explores that was opened while the smart client assembly download is still open the assembly file can't be removed (gacutil /cdl). Just after closing all explorers window we managed to down load smart client assembly and saw it using gacutil. I've no idea why opened explorer windows should influence explorer window that that he is the chosen one (to download smart client assembly J ).